Speculative fix for DOM manipulation using standalone xmldom library

[rathboma]

Replaces browser-built-in DOM libs with xmldom. Should fix issues using library in webworkers. Testing now.

Also, you guys really should commit a package-lock.json or a yarn.lock file to make sure your resolved dependencies don't change between machines. I've added a yarn.lock, because I use yarn, but that's up to you.

Fix #401

[ghost]

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[jeremymeng]

@rathboma Thanks for the PR! However, in general we try to avoid adding additional dependencies for browser users as it unnecessarily increases the bundle size for users who don't need XML feature. This is why we suggest polyfilling the DOM api as a workaround.

[jeremymeng]

@rathboma a polyfill workaround would be similar to the one in https://github.com/Azure/azure-sdk-for-js/blob/589ce99c13a16de07dd8e9dc2117cd3e44666d4d/samples/web-workers/js/polyfill.worker.js. I am closing this PR. Please let us know if you have any further questions.